DC/DC voltage regulators generally consist of a reference system, a clock generator, and a boosting/bucking circuit. The regulator receives an input voltage and generates a boosted (stepped-up) or bucked (stepped-down) voltage as an output. In certain applications, such as memory or LED drivers, an input voltage is provided at a predetermined supply or ground and an output is a positive voltage higher than the supply voltage or a negative voltage less than the ground voltage.
A boosting/bucking circuit can be activated according to a reference system to produce an output at a predetermined level. The reference system determines the accuracy of the output. Current reference systems can utilize one or more architectures, such as a voltage comparator including a tapped output compared to a predetermined reference voltage or a level shifter configured to compare a segmented level voltage to a reference voltage.
Current reference systems generate large ripples and die-to-die inaccuracies in an average output voltage due to process variations. The process variations are caused by process deviations such as variations in device (e.g., MOS and/or resistor) dimensions, threshold voltage, mismatch in MOS/resistor ladders, and/or other sources. If the reference system has a variation from a predetermined level, the output cannot be set to a reliable level.